RESUMO
OBJECTIVE: This study evaluated the influence of Nd:YAG laser on the evaporation degree (ED) of the solvent components in total-etch and self-etch adhesives. MATERIALS AND METHODS: The ED of Gluma Comfort Bond (Heraeus-Kulzer) one-step self-etch adhesive, and Adper Single Bond 2 (3M ESPE), and XP Bond (Dentsply) total-etch adhesives was determined by weight alterations using two techniques: Control--spontaneous evaporation of the solvent for 5 min; Experimental--Nd:YAG laser irradiation for 1 min, followed by spontaneous evaporation for 4 min. The weight loss due to evaporation of the volatile components was measured at baseline and after 10 s, 20 s, 30 s, 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s, 110 s, 2 min, 3 min, 4 min, and 5 min. RESULTS: Evaporation of solvent components significantly increased with Nd:YAG laser irradiation for all adhesives investigated. Gluma Comfort Bond showed significantly higher evaporation of solvent components than Adper Single Bond 2 and XP Bond. All the adhesives lost weight quickly during the first min of Nd:YAG laser irradiation. CONCLUSION: The application of Nd:YAG laser on adhesives before light curing had a significant effect on the evaporation of the solvent components, and the ED of Gluma Comfort Bond one-step self-etch adhesive was significantly higher than with Adper Single Bond 2 and XP Bond total-etch adhesives. CLINICAL RELEVANCE: The use of the Nd:YAG laser on the uncured adhesive technique can promote a greater ED of solvents, optimizing the longevity of the adhesive restorations.
Assuntos
Adesivos Dentinários/química , Lasers de Estado Sólido , Solventes/química , Cimentos Dentários/química , Cimentos Dentários/efeitos da radiação , Adesivos Dentinários/efeitos da radiação , Humanos , Umidade , Cura Luminosa de Adesivos Dentários/métodos , Teste de Materiais , Transição de Fase , Solventes/efeitos da radiação , Temperatura , Fatores de Tempo , VolatilizaçãoRESUMO
4-Aminoimidazole-5-carbonitrile (AICN) was suggested as a prebiotically plausible precursor of purine nucleobases and nucleotides. Although it can be formed in a sequence of photoreactions, AICN is immune to further irradiation with UV-light. We present state-of-the-art multi-reference quantum-chemical calculations of potential energy surface cuts and conical intersection optimizations to explain the molecular mechanisms underlying the photostability of this compound. We have identified the N-H bond stretching and ring-puckering mechanisms that should be responsible for the photochemistry of AICN in the gas phase. We have further considered the photochemistry of AICN-water clusters, while including up to six explicit water molecules. The calculations reveal charge transfer to solvent followed by formation of an H3O(+) cation, both of which occur on the (1)πσ* hypersurface. Interestingly, a second proton transfer to an adjacent water molecule leads to a (1)πσ*/S0 conical intersection. We suggest that this electron-driven proton relay might be characteristic of low-lying (1)πσ* states in chromophore-water clusters. Owing to its nature, this mechanism might also be responsible for the photostability of analogous organic molecules in bulk water.
Assuntos
Imidazóis/química , Modelos Químicos , Modelos Moleculares , Nitrilas/química , Prebióticos , Purinas/química , Solventes/química , Simulação por Computador , Imidazóis/efeitos da radiação , Luz , Teste de Materiais , Nitrilas/efeitos da radiação , Fotoquímica/métodos , Purinas/efeitos da radiação , Solventes/efeitos da radiaçãoRESUMO
We investigate the acid-base proton exchange reaction in a microsolvated bifunctional chromophore by means of quantum chemical calculations. The UV/vis spectroscopy shows that equilibrium of the keto- and enol-forms in the electronic ground state is shifted to the keto conformation in the excited state. A previously unknown mechanism involving a hydroxide ion transport along a short water wire is characterized energetically, which turns out to be competitive with the commonly assumed proton transport. Both mechanisms are shown to have a concerted character, as opposed to a step-wise mechanism. The alternative mechanism of a hydrogen atom transport is critically examined, and evidence for strong solvent dependence is presented. Specifically, we observe electrostatic destabilization of the corresponding πσ* state by the aqueous solvent. As a consequence, no conical intersections are found along the reaction pathway.
Assuntos
Radical Hidroxila/química , Hidroxiquinolinas/química , Microfluídica/métodos , Modelos Químicos , Teoria Quântica , Solventes/química , Água/química , Simulação por Computador , Hidroxiquinolinas/efeitos da radiação , Luz , Prótons , Solventes/efeitos da radiaçãoRESUMO
The transformation of the synthesized allicin, using conventional method, the influence of ultrasound and microwaves, in different organic solvents (acetonitrile, acetone, methanol, and chloroform), at various temperatures (room temperature, 45 °C, and 55 °C) was investigated. Allicin degradation kinetic was monitored by HPLC. Allicin transformation under the effect of microwaves is faster than transformations performed under the influence of ultrasound or by conventional method. Increase of the temperature accelerates allicin transformation. Pharmacologically active compounds of (E)-ajoene, (Z)-ajoene, 3-vinyl-4H-1,2-dithiin, 2-vinyl-4H-1,3-dithiin, and diallyl disulfide were isolated from the mixture of transformation products of allicin under the influence of microwaves in methanol at 55 °C, which is according to kinetic parameters (highest values of the order of reaction and the lowest activation energy) the optimal method.
Assuntos
Dissulfetos/síntese química , Solventes/química , Ácidos Sulfínicos/química , Ácidos Sulfínicos/efeitos da radiação , Dissulfetos/efeitos da radiação , Ondas de Choque de Alta Energia , Micro-Ondas , Doses de Radiação , Solventes/efeitos da radiação , Sulfóxidos , TemperaturaRESUMO
INTRODUCTION: In the nuclear industry 1,4-dioxane is used as a solvent in liquid scintillation technique for measuring low-energy beta-emitters such as ³H or C¹4 in aqueous media. Improper disposal of 1,4-dioxane can contaminate the ground and surface waters. Conventional wastewater treatment processes like chemical treatment, air stripping, carbon adsorption, and biological treatment are ineffective for the degradation of 1,4-dioxane. METHODS: In the present study, the kinetics of degradation of 1,4-dioxane using advanced oxidation processes viz., H2O2 alone, Fe(II) + H2O2, UV (15 W) + H2O2, UV (15 W) + Fe(II) + H2O2, US (130 KHz) + Fe(II) + H2O2, and sunlight + Fe(II) + H2O2 at pH 3.0 was investigated. The optimization of Fe (II) for the processes using Fe (II) + H2O2 was carried out. CONCLUSIONS: The kinetics of degradation using sunlight + Fe (II) + H2O2 was found to be fastest when compared to the other processes. The degradation was found to follow first-order kinetics. Formation of acidic intermediates was suspected from the observed pH changes during the degradation processes.
Assuntos
Dioxanos/química , Oxidantes/química , Solventes/química , Ácido Acético/análise , Dioxanos/análise , Dioxanos/efeitos da radiação , Estudos de Viabilidade , Peróxido de Hidrogênio/química , Concentração de Íons de Hidrogênio , Hidrólise/efeitos dos fármacos , Hidrólise/efeitos da radiação , Ferro/química , Cinética , Oxirredução , Fotólise , Contagem de Cintilação , Solventes/análise , Solventes/efeitos da radiação , Luz Solar , Ultrassom/métodos , Raios Ultravioleta , Poluição Química da Água/prevenção & controleRESUMO
Nano-structures of AgBr have been prepared by reaction between AgNO(3) and KBr under ultrasound irradiation. Particle sizes and morphology of nanoparticle are depending on temperature, power of sonicating, reaction time and concentration. The effects of these parameters in growth and morphology of the nano-structures have been studied. Results suggest that an increasing of temperature, sonication power and concentration led to a decreasing of particle size. The samples were characterized with powder X-ray diffraction (XRD) and scanning electron microscopy (SEM).
Assuntos
Brometos/química , Brometos/efeitos da radiação , Nanoestruturas/química , Nanoestruturas/efeitos da radiação , Compostos de Prata/química , Compostos de Prata/efeitos da radiação , Solventes/química , Sonicação/métodos , Ondas de Choque de Alta Energia , Teste de Materiais , Nanoestruturas/ultraestrutura , Tamanho da Partícula , Doses de Radiação , Solventes/efeitos da radiação , Propriedades de SuperfícieRESUMO
This work reports the transesterification of soybean oil with ethanol using two commercial immobilized lipases under the influence of ultrasound irradiation. The experiments were performed in an ultrasonic water bath, following a sequence of experimental designs to assess the effects of temperature, enzyme and water concentrations, oil to ethanol molar ratio and output irradiation power on the reaction yield. Results show that ultrasound-assisted lipase-catalyzed transesterification of soybean oil with ethanol might be a potential alternative route to conventional alkali-catalyzed method, as high reaction yields (~90 wt.%) were obtained at mild irradiation power supply (~100 W), and temperature (60 °C) in a relatively short reaction time, 4h, using Lipozyme RM IM as catalyst. The repeated use of the catalyst under the optimum experimental condition resulted in a decay in both enzyme activity and product conversion after two cycles. The use of Novozym 435 led to lower conversions (about 57%) but the enzyme activity was stable after eight cycles of use, showing, however, a reduction in product conversion after the forth cycle.
Assuntos
Lipase/química , Lipase/efeitos da radiação , Compostos Orgânicos/química , Compostos Orgânicos/efeitos da radiação , Sonicação/métodos , Óleo de Soja/química , Óleo de Soja/efeitos da radiação , Ativação Enzimática/efeitos da radiação , Enzimas Imobilizadas , Esterificação/efeitos da radiação , Proteínas Fúngicas , Ondas de Choque de Alta Energia , Cinética , Doses de Radiação , Solventes/química , Solventes/efeitos da radiação , Especificidade por Substrato/efeitos da radiaçãoRESUMO
Ruthenium-exchanged FAU-Y zeolite (RuY) was used as a recyclable catalyst for regioselective ring-opening of epoxides with indoles under irradiation of sonic waves. It was found that a solvent free process, under the above mentioned conditions provides good yields of the desired 3-alkylated indole derivatives.
Assuntos
Compostos de Epóxi/química , Compostos de Epóxi/efeitos da radiação , Rutênio/química , Rutênio/efeitos da radiação , Sonicação/métodos , Zeolitas/química , Zeolitas/efeitos da radiação , Catálise/efeitos da radiação , Ondas de Choque de Alta Energia , Indóis/química , Indóis/efeitos da radiação , Doses de Radiação , Solventes/química , Solventes/efeitos da radiaçãoRESUMO
Given earlier observations that microwave frequencies can have a substantial effect on the photoactivity of a well-known photocatalyst (TiO(2)), in the synthesis of 3,6-diphenyl-4-n-butylpyridazine through a Diels-Alder process, and in the one-pot solvent-free synthesis of a room-temperature ionic liquid, we proceeded to examine the frequency effects of the 5.8 and 2.45 GHz microwave (MW) radiation in the synthesis of gold nanoparticles in non-polar media, such as oleylamine, which have a low dielectric constant (ε'), and we further examine differences in shape and size under otherwise identical temperature conditions when the synthesis of the gold nanoparticles was carried out in an ethylene glycol polar medium in the presence of polyvinylpyrrolidone. Whereas a change in microwave frequency from 2.45 to 5.8 GHz at equal microwave power levels led to the synthesis of gold nanoparticles in the non-polar media, a change in the microwave frequency had no effect on the size and shape of the gold nanoparticles synthesized in polar media for identical microwave power levels.
Assuntos
Ouro/química , Ouro/efeitos da radiação , Nanoestruturas/química , Nanoestruturas/efeitos da radiação , Coloides/química , Coloides/efeitos da radiação , Substâncias Macromoleculares/química , Substâncias Macromoleculares/efeitos da radiação , Teste de Materiais , Micro-Ondas , Conformação Molecular/efeitos da radiação , Nanoestruturas/ultraestrutura , Tamanho da Partícula , Solventes/química , Solventes/efeitos da radiação , Eletricidade Estática , Propriedades de Superfície/efeitos da radiaçãoRESUMO
The action of high intensity cavitation on several liquid halocarbons (C(2)Cl(4) CCl(4), CHCl(3), C(2)H(2)Br(4)) and other organic solvents (acetone, benzene and their mixtures) was investigated by recording multibubble sonoluminescence UV-Vis spectra over the temperature range between 246 and 298 K. The temperature induced variation of some thermophysical properties of the solvents Favours the interpretations of their role in determining the salient characteristics of the recorded spectra. We observed that high volatility does not necessarily quench sonoluminescence emission and that argon flow plays a key role in the appearance of radical emission lines. While for each investigated substance the intensity of C*(2) emission lines was clearly correlated to temperature, a comparative test between different halocarbons did not show a clear correlation with vapour pressure. Following recently reported results which evidenced the formation of dynamically differentiated populations of emitting bubbles in sulphuric acid, we performed MBSL experiments in liquid mixtures of halocarbons and sulphuric acid to investigate the correlation between the production of emitting species and the halocarbon volatility.
Assuntos
Medições Luminescentes/métodos , Compostos Orgânicos/química , Compostos Orgânicos/efeitos da radiação , Solventes/química , Solventes/efeitos da radiação , Sonicação/métodos , Microbolhas , Doses de Radiação , Pressão de VaporRESUMO
Mild and efficient Fischer esterification reactions of lactic acid with a variety of straight chain aliphatic alcohols, cyclohexanol and benzyl alcohol were successfully performed using two novel Brønsted acidic ionic liquids that bear an aromatic sulfonic acid group on the imidazolium or pyridinium cation under ultrasound irradiation. These reactions carried out smoothly with good to excellent conversion rate (78-96%) and satisfactory yields (73-92%) in shorter reaction time (4-6h) at room temperature when the amount of ionic liquids was 20 mol%. These ionic liquids could be recovered readily and recycled five times without any significant loss in their catalytic activity.
Assuntos
Líquidos Iônicos/química , Líquidos Iônicos/efeitos da radiação , Ácido Láctico/síntese química , Ácido Láctico/efeitos da radiação , Sonicação , Sulfatos/química , Sulfatos/efeitos da radiação , Ácidos/química , Ácidos/efeitos da radiação , Ésteres/química , Ésteres/efeitos da radiação , Solventes/química , Solventes/efeitos da radiaçãoRESUMO
1-Hexanesulphonic acid sodium salt was found to be an efficient catalyst for the green synthesis of alpha-aminophosphonates by the coupling of aldehydes/ketone, an amine and triethyl phosphite under ultrasound irradiation at ambient temperature for appropriate time to furnish the desired product in good to excellent yield under solvent-free condition. This catalyst provides clean conversion; greater selectivity and easy workup make this protocol practical and economically attractive.
Assuntos
Ácidos Alcanossulfônicos/química , Ácidos Alcanossulfônicos/efeitos da radiação , Organofosfonatos/síntese química , Organofosfonatos/efeitos da radiação , Sonicação , Catálise/efeitos da radiação , Sais/química , Sais/efeitos da radiação , Sódio/química , Sódio/efeitos da radiação , Solventes/química , Solventes/efeitos da radiaçãoRESUMO
Montmorillonite K-10 and KSF were found to be highly efficient, environmentally friendly and recyclable heterogeneous catalysts for the selective synthesis of a variety of 2-aryl-5,6-dihydro-4H-1,3-oxazines from arylnitriles and 3-amino-1-propanol under ultrasound irradiation. This new methodology provides excellent yields in short reaction times (10-25 min). The reaction work-up is very simple and the catalysts can be easily separated from the reaction mixture and reused several times in subsequent reactions. This catalytic system also exhibits excellent chemoselectivity in the synthesis of mono-oxazines from dinitriles.
Assuntos
Silicatos de Alumínio/química , Bentonita/química , Oxazinas/síntese química , Oxazinas/efeitos da radiação , Solventes/química , Sonicação , Silicatos de Alumínio/efeitos da radiação , Bentonita/efeitos da radiação , Argila , Solventes/efeitos da radiaçãoRESUMO
Highly crystalline metal oxide nanoparticles of TiO(2), WO(3), and V(2)O(5) were synthesized in just a few minutes by reacting transition metal chloride with benzyl alcohol using ultrasonic irradiation under argon atmosphere in a non-aqueous solvent. The sonochemical process was conducted at a relatively low temperature, 363 K. A unique crystallization process of these nanoparticles has been observed and characterized by powder X-ray diffraction (PXRD), high resolution scanning electron microscopy (HRSEM), and BET. The particles' size and shape measured from HRSEM reveal "quasi" zero-dimensional, spherical TiO(2) particles in the range of 3-7 nm. The V(2)O(5) particles have a "quasi" one-dimensional ellipsoidal morphology, with lengths in the range of 150-200 nm and widths varying between 40 and 60 nm. The WO(3) particles were obtained as "quasi" two-dimensional platelets with square shapes having facets ranging from 30 to 50 nm. The thickness of these platelets was between 2 and 7 nm. The mechanism of the reactions leading to these three metal oxide nanoparticles in a non-aqueous system is substantiated by Nuclear Magnetic Resonance (NMR), and Electron Spin Resonance (ESR).
Assuntos
Metais/química , Metais/efeitos da radiação , Nanoestruturas/química , Nanoestruturas/efeitos da radiação , Óxidos/química , Óxidos/efeitos da radiação , Sonicação/métodos , Cristalização/métodos , Nanoestruturas/ultraestrutura , Tamanho da Partícula , Doses de Radiação , Solventes/química , Solventes/efeitos da radiação , Água/químicaRESUMO
This paper presents a novel solvent free method of synthesis of trans-chalcones. The method was based on ultrasound irradiation of the reagents (aryl methyl ketones and aryl aldehydes) in presence of commercial acid-montmorillonites as catalysts. The trans-chalcones were synthesized in high yields (85-95%) and excellent selectivity in a short reaction time.
Assuntos
Silicatos de Alumínio/química , Silicatos de Alumínio/efeitos da radiação , Chalconas/síntese química , Chalconas/efeitos da radiação , Sonicação/métodos , Ácidos/química , Ácidos/efeitos da radiação , Catálise , Argila , Doses de Radiação , Solventes/química , Solventes/efeitos da radiaçãoRESUMO
Photochemically induced dynamic nuclear polarization (photo-CIDNP) of nuclei other than (1)H offers a tremendous potential for sensitivity enhancement in liquid state NMR under mild, physiologically relevant conditions. Photo-CIDNP enhancements of (15)N magnetization are much larger than those typically observed for (1)H. However, the low gyromagnetic ratio of (15)N prevents a full fruition of the potential signal-to-noise gains attainable via (15)N photo-CIDNP. Here, we propose two novel pulse sequences, EPIC- and CHANCE-HSQC, tailored to overcome the above limitation. EPIC-HSQC exploits the strong (1)H polarization and its subsequent transfer to non-equilibrium N(z) magnetization prior to (15)N photo-CIDNP laser irradiation. CHANCE-HSQC synergistically combines (1)H and (15)N photo-CIDNP. The above pulse sequences, tested on tryptophan (Trp) and the Trp-containing protein apoHmpH, were found to display up to 2-fold higher sensitivity than the reference NPE-SE-HSQC pulse train (based on simple (15)N photo-CIDNP followed by N-H polarization transfer), and up to a ca. 3-fold increase in sensitivity over the corresponding dark pulse schemes (lacking laser irradiation). The observed effects are consistent with the predictions from a theoretical model of photo-CIDNP and prove the potential of (15)N and (1)H photo-CIDNP in liquid state heteronuclear correlation NMR.
Assuntos
Espectroscopia de Ressonância Magnética/métodos , Radioisótopos de Nitrogênio/análise , Radioisótopos de Nitrogênio/química , Fotoquímica/métodos , Solventes/química , Triptofano/análise , Triptofano/química , Algoritmos , Luz , Radioisótopos de Nitrogênio/efeitos da radiação , Sensibilidade e Especificidade , Processamento de Sinais Assistido por Computador , Solventes/efeitos da radiação , Triptofano/efeitos da radiaçãoRESUMO
12 hybrid photocatalysts consisting of titania (TiO(2)) and an adsorbent such as mordenite were investigated for the photocatalytic decomposition of toluene, a major indoor contaminant in indoor air. The highest decomposition rate was obtained with the use of mordenite and silicon dioxide (SiO(2)) as additives to TiO(2). The photocatalytic activities of hybrid photocatalysts in decomposing toluene are 1.33 times as high as pure P25 at the net weight loading of 0.49 mg/cm(2) under the test condition. Scanning electron microscopy (SEM) images confirmed that the hybrid photocatalyst films were very porously distributed; TiO(2) was adsorbed on the surface of mordenite and SiO(2), increasing the reaction area of TiO(2). The unimolecular Langmuir-Hishelwood model and mass-transfer-based (MTB) method were used to evaluate the reaction coefficients and adsorption equilibrium coefficients of hybrid photocatalysts. It is evidenced that the reaction areas of two hybrid photocatalysts were 1.52 and 1.64 times larger than that of P25, respectively, which is the major reason to make the high removal efficiency of toluene.
Assuntos
Poluentes Atmosféricos/química , Poluição do Ar em Ambientes Fechados/prevenção & controle , Processos Fotoquímicos , Titânio/química , Tolueno/química , Adsorção , Poluentes Atmosféricos/efeitos da radiação , Silicatos de Alumínio , Gases/química , Solventes/química , Solventes/efeitos da radiação , Tolueno/efeitos da radiaçãoRESUMO
A factor currently limiting the clinical utility of x-ray CT polymer gel dosimetry is the overall low dose sensitivity (and hence low dose resolution) of the system. Hence, active research remains in the investigation of polymer gel formulations with increased CT dose response. An ideal polymer gel dosimeter will exhibit a sensitive CT response which is linear over a suitable dose range, making clinical implementation reasonably straightforward. This study reports on the variations in rate and form of the CT dose response of irradiated polymer gels manufactured with glycerol, which is a co-solvent that permits dissolution of additional bisacrylamide above its water solubility limit (3% by weight). This study focuses on situations where the concentration of bisacrylamide is kept at or below its water solubility limit so that the influence of the co-solvent on the dose response can be explored separately from the effects of increased cross-linker concentration. CT imaging and Raman spectroscopy are used to construct dose-response curves for irradiated gels varying in (i) initial total monomer (%T) and (ii) initial co-solvent concentration. Results indicate that: (i) for a fixed glycerol concentration, gel response increases linearly with %T. Furthermore, the functional form of the dose response remains constant, in agreement with a previous model of polymer formation. (ii) Polymer gels with constant %T and increasing co-solvent concentrations also show enhanced CT response. In addition, the functional form of the response is altered in these gels as co-solvent concentration is increased. Raman data indicate that the fraction of bis-acrylamide incorporated into polymerization, as opposed to cyclization, increases as co-solvent concentration increases. The changes in functional form indicate varying polymer yields (per unit dose), akin to relative fractional monomer/cross-linker (i.e. %C) changes in earlier studies. These results are put into context of the model of polymer formation. The implications of these results on the clinical utility of polymer gels with co-solvent are highlighted.
Assuntos
Glicerol/química , Polímeros/química , Polímeros/efeitos da radiação , Radiometria/métodos , Ressonância de Plasmônio de Superfície/métodos , Tomografia Computadorizada por Raios X/métodos , Relação Dose-Resposta à Radiação , Géis/química , Géis/efeitos da radiação , Glicerol/efeitos da radiação , Teste de Materiais , Doses de Radiação , Solventes/química , Solventes/efeitos da radiaçãoRESUMO
Ultraviolet-visible and infrared transient-absorption spectroscopy are used to investigate the transfer of energy from nitrite to water during the photo-dissociation of NO2-(aq). Nitrite is dissociated by photo-excitation at 200 nm. About 40% of the photo-fragments recombine and relax on a 3 ps timescale, while diffusive recombination accounts for another 10% of the fragments during the subsequent 50 ps. The infrared transient-absorption spectra of the photo-dissociation of nitrite solvated in H2O and D2O show no evidence of excited vibrations after 0.5 ps. Instead they reveal a sub-0.5 ps change in the infrared absorption similar to what is observed when the temperature of water is increased. Since this spectral change is associated with the weakening of the hydrogen-bond network, we infer that excess energy from the dissociation of nitrite is dissipated to the local hydrogen-bonded water network in less than 0.5 ps. The rapid change in the infrared absorption is followed by a slower (50 ps) component associated with the energy dissipation to the solvent as the photo-fragments diffusively recombine and relax.
Assuntos
Óxido de Deutério/química , Óxido de Deutério/efeitos da radiação , Nitritos/química , Nitritos/efeitos da radiação , Raios Ultravioleta , Transferência de Energia , Fotoquímica , Teoria Quântica , Solubilidade , Solventes/química , Solventes/efeitos da radiação , Espectrofotometria Infravermelho/métodos , Espectrofotometria Ultravioleta/métodos , Fatores de Tempo , Água/químicaRESUMO
Steady-state and nanosecond laser flash photolysis measurements of 4-methoxybenzyl alcohol (1a), 4-methoxy-alpha-methylbenzyl alcohol (1b), 4,4'-dimethoxydiphenylmethanol (1c) and 4-methoxy-alpha,alpha'-dimethylbenzyl alcohol (1d) were carried out in air-equilibrated CH(2)Cl(2) and CH(3)CN solutions, in the presence of 9,10-dicyanoanthracene (DCA) and N-methylquinolinium tetrafluoroborate (NMQ(+)BF(4)(-)) as sensitizers. In particular, steady-state irradiation with DCA produced carbonyl compounds and, with NMQ(+)BF(4)(-), carbonyl compounds, ethers (substrates 1a-c ) and styrene (substrate 1d ) while time-resolved investigations gave evidence of charged species produced upon irradiation. The effect of solvent polarity on the reactivity was investigated; in the case of DCA, the reactivity increased with the solvent polarity, while the opposite was obtained when NMQ(+)BF(4)(-) was used. Quantum mechanical calculations at semiempirical (INDO/1-CI) and DFT (B3LYP/6-311G(d)) levels were used to support transient assignments and to obtain the charge and spin density distributions, respectively. The different photooxidation mechanisms operative with the neutral and charged sensitizer were rationalized in terms of the reactivity of free and complexed radical cations, respectively.